Currently developed wireless (radio) technology of the 5th generation (5G) is aimed at supporting a large range of use case, including such with requirements for low latency. On the other hand, 5G technology is being developed to be allow flexibility in transmission timing structures, and to utilize a wide frequency range. If carriers of significantly different frequencies are being utilized, transmission timings may be significantly different due to the different physical characteristics like bandwidth/spacing and symbol time length.
With these demands, new problems and challenges arise for example in the context of ARQ/HARQ processes.